The invention relates to an ultrasonically driven, rotary device and, more particularly, a rotary dental polisher device.
One of the most widely accepted new dental instruments of recent years is the ultrasonic dental prophylaxis device. Such devices have a power unit which converts AC line-frequency electrical power into higher frequencies and a flexible cable which carries the higher frequency power to a handheld, tubular housing. An insert for the device has a sleeve for releasably connecting the insert to the housing and for supporting a vibrator. One end of the vibrator projects into the housing and is a magnetostrictive or other transducer device responsive to the higher frequency electrical power in the housing for producing longitudinal ultrasonic vibrations in the vibrator. The other end of the vibrator is the dental tool. The two ends of the vibrator are usually connected by a connecting body which, by a reduction in diameter or change in acoustic properties, amplifies the ultrasonic vibrations at the tool. The whole vibrator is also an integral multiple of one-half the wavelength of the ultrasonic vibrations in the vibrator to be resonant for maximum vibration and to have at least one node of ultrasonic vibration. The sleeve is usually arranged to support the vibrator at the node to avoid damping the vibrations.
The tool end of the vibrator has at least one bend which converts the longitudinal ultrasonic vibrations in the vibrator into ultrasonic elliptical motion at the tool end as described in the assignee's U.S. Pat. No. 2,990,616. The elliptical motion of the tool is then used to dislodge ultrasonically calculus, plaque and other matter adhered to teeth, particularly along the gum line. Removing calculus and plaque from teeth by hand is well known for the periodontal and hygienic treatment of teeth, and the ultrasonic dental prophyalaxis unit provides similar treatment with the improvement and assistance of ultrasonic vibrations.
In addition to removing calculus and plaque, however, teeth often require polishing or abrasive brushing to remove stains and otherwise clean broader areas of the teeth more rapidly. Such polishing is generally done with a relatively low-speed rotary rubber cup or brush and a polishing compound. Periodontists and hygienists have thus required two pieces of equipment: the ultrasonic dental prophylaxis device and a rotary polisher.
Rotary polishers have, until now, generally been driven by dental drilling equipment, but the very high rotational speeds (on the order of 10.sup.5 rpm) of modern high speed air turbine dental drills, while desirable for dental drilling, are greatly in excess of the rotational speeds suitable for the rotary brushing or polishing of teeth. One limitation on the speeds of such rotary polishing, for example, is retaining the polishing compound on the rotating brush. For this, rotational speeds on the order of 10.sup.2 to 10.sup.3 rpm are desired. If the more recent air turbine drive is thus to be used for rotary polishing, an expensive speed reduction device must be provided to achieve the much lower rotary polishing speeds, and an air power source also must be provided.
Alternatively, the old-fashioned, variable-speed, electrical, belt-driven dental drilling apparatus may be used, but such devices with their large, multi-arm belt structures are particularly intimidating to patients. In addition, three pieces of equipment and two power supplies are then required for a full dental operatory: the electric ultrasonic prophylaxis unit for removing calculus and plaque, the high-speed turbine drill and air power supply, and the electric belt unit for polishing.
There has thus been for some years a desire to consolidate dental drilling, polishing and ultrasonic cleaning devices for economic and psycholological advantage. This desire, however, has so far led only to suggestions of combining the rotary drilling and polishing functions with the disadvantages just described, or to combining the ultrasonic prophylaxis and high-speed rotary drilling functions as described in the assignee's U.S. Pat. No. 3,058,218. This patent discloses a way of rotating a drill at high speeds through longitudinal ultrasonic vibrations. The longitudinal ultrasonic vibrations are produced at one end of a resonant vibrator insert plugged into a housing with energizing means and converted into elliptical motion at the other end of the vibrator in the same way as described for the ultrasonic dental prophylaxis device. The elliptically-moving end of the vibrator tangentially engages a shaft, which is rotatably mounted in or adjacent to the vibrating tip during one arc of the ellipse. The high frequency of the ultrasonic vibrations, generally in a range of from 15 to 50 KHZ, however, rotates the shaft at correspondingly high speeds of from 45,000 to 360,000 rpm in the examples in the patent. Such speeds are greatly in excess of those suitable for rotary polishing, at least because the polishing compound cannot be retained on the polisher. Thus, even though the patent initially suggests using the ultrasonically driven rotary device for "abrading and polishing operations", such operations must be considered grinding-type polishing and not the brushing-type polishing for cleaning teeth considered here. This is further confirmed by the patent's consistent emphasis of high rotational speeds, as opposed to the low speeds desired for polishing.
The patent also discloses only rotating the drill shaft directly from the elliptically-moving end of the vibrator. As the elliptical motion tangentially engages the shaft during one arc of the ellipse to rotate the shaft unidirectionally it must impart some radial thrust to the shaft to achieve the tangential driving engagement. In use, however, the rotated polisher tool shaft or drill has some axial thrust applied to it. It has been found difficult, at least economically, to provide a bearing for a directly rotated element or elements as disclosed in the patent which will endure these radial and axial thrusts in the presence of ultrasonic vibrations. The relatively bulky and costly bearings necessary to try to accomodate the combined radial and axial thrusts also absorbed substantial power which could be preserved for the rotary output if the bearing loads could be reduced to reduce the required bearing strength and bulk. Thus, for these practical reasons, too, the device disclosed in the patent is not suitable for a rotary low-speed or brush-type polisher.
Rotating the drill shaft directly from the elliptically-moving end of the vibrator also required offsetting the drill shaft from the longitudinal axis of the vibrator to achieve the drill-rotating tangential engagement with the vibrator. Locating the rotated (drill) shaft on the axis of the vibrator, however, would make the device both easier to use and through proper design still further reduce the shaft bearing requirements by eliminating the torque exerted on the insert (and handpiece) by the axial forces.